Linear Motor and Lithography Arrangement Including Linear Motor

ABSTRACT

A lithographic apparatus including a uniformity correction system is disclosed. The lithographic apparatus comprises an illumination system configured to condition a beam of radiation. The illumination system comprises a uniformity correction system located at a plane configured to receive a substantially constant pupil when illuminated with the beam of radiation. The uniformity correction system includes fingers configured to be movable into and out of intersection with a radiation beam so as to correct an intensity of respective portions of the radiation beam. A linear motor actuator arrangement drives the fingers to their respective appropriate positions to compensate for non-uniform illumination. Control is provided by a control system that precisely manipulates carriers of the fingers.

This application incorporates by reference in their entireties U.S.patent application Ser. No. 13/473,547, filed May 16, 2012 and U.S.Provisional Patent Application No. 61/532,886, filed Sep. 9, 2011.

BACKGROUND

1. Field of Invention

The invention relates to a lithographic apparatus and illuminationuniformity correction system. The present invention generally relates tolithography and more particularly to correcting for illuminationirregularities so as to produce a uniform beam in a cross scan directionduring lithography of an integrated circuit.

2. Related Art

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. The lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning device, which is alternatively referredto as a mask or a reticle, may be used to generate a circuit patterncorresponding to an individual layer of the IC, and this pattern can beimaged onto a target portion (e.g., comprising part of, one or severaldies) on a substrate (e.g., a silicon wafer) that has a layer ofradiation-sensitive material (resist). In general, a single substratewill contain a network of adjacent target portions that are successivelyexposed. Known lithographic apparatus include so-called steppers, inwhich each target portion is irradiated by exposing an entire patternonto the target portion in one go, and so-called scanners, in which eachtarget portion is irradiated by scanning the pattern through the beam ina given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti parallel to this direction.

A lithographic apparatus typically includes an illumination system,which is arranged to condition radiation generated by a radiation sourcebefore the radiation is incident upon a patterning device. Theillumination system may, for example, modify one or more properties ofthe radiation, such as polarization and/or illumination mode. Theillumination system may include a uniformity correction system, which isarranged to correct or reduce non-uniformities, e.g., intensitynon-uniformities, present in the radiation. The uniformity correctiondevices may employ actuated fingers which are inserted into an edge of aradiation beam to correct intensity variations. However, a width of aspatial period of intensity variation that can be corrected is dependenton a size of an actuating device used to move fingers of the uniformitycorrection system. Furthermore, in some instances, if a size or shape ofthe fingers used to correct irregularities of a radiation beam ismodified, then the uniformity correction system may compromise or modifyin an unwanted manner one or more properties of the radiation beam, suchas a pupil formed by the radiation beam.

Lithography is widely recognized as a key process in manufacturingintegrated circuits (ICs) as well as other devices and/or structures. Alithographic apparatus is a machine, used during lithography, whichapplies a desired pattern onto a substrate, such as onto a targetportion of the substrate. During manufacture of ICs with a lithographicapparatus, a patterning device (which is alternatively referred to as amask or a reticle) generates a circuit pattern to be formed on anindividual layer in an IC. This pattern may be transferred onto thetarget portion (e.g., comprising part of, one, or several dies) on thesubstrate (e.g., a silicon substrate). Transfer of the pattern istypically via imaging onto a layer of radiation-sensitive material(e.g., resist) provided on the substrate. In general, a single substratecontains a network of adjacent target portions that are successivelypatterned. To reduce manufacturing cost of ICs, it is customary toexpose multiple substrates of each IC. Likewise, it is also customarythat the lithographic apparatus is in almost constant use. That is, inorder to keep manufacturing cost of all types of ICs at a potentialminimum, the idle time between substrate exposures is also minimized. Asa result, the lithographic apparatus absorbs heat which causes expansionof the apparatus's components leading to drift, movement, and uniformitychanges.

In order to ensure good imaging quality on the patterning device and thesubstrate, it is beneficial to minimize or eliminate illuminationirregularities. One way that this is carried out is by inserting“fingers” into an illumination beam at appropriate places to even outillumination. Various electro-mechanical sub-systems arrangements areutilized or proposed to manipulate the fingers into the appropriatepositions for beam scanning and to move those fingers out of the beampath when they are not needed.

The market demands that sub-systems for manipulating the positions offingers reliably operate in the environment of a lithography device sothat the lithographic apparatus can perform lithography processes asefficiently as possible to maximize manufacturing capacity and keepmanufacturing costs per device and maintenance low.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIGS. 1A and 1B respectively depict reflective and transmissivelithographic apparatuses with uniformity compensators and associatedsensors.

FIG. 2 is a schematic diagram of an example extreme ultra violet (EUV)lithographic apparatus.

FIG. 3 is an exploded view of a mechanical portion of a IIC sub-system300 compensator sub-system having “fingers” that are moved intopositions within a projected beam to promote uniformity.

FIG. 4 is a cut-away perspective view of the structure of a portion ofthe compensator sub-system and indicating directions of movement in use.

FIG. 5 is a block diagram of a control system for operating thecompensator sub-system shown in FIGS. 3 and 4.

FIG. 6 is a schematic diagram of an embodiment of a linear motorarrangement that can be substituted for a portion of the compensatorsub-system shown in FIGS. 3 and 4.

FIG. 7 is a schematic diagram of an embodiment of a linear motorarrangement that can be substituted for a portion of the compensatorsub-system shown in FIGS. 3 and 4.

FIG. 8 is a block diagram of a control system for operating thecompensator sub-system including the embodiments shown in FIGS. 6 and 7.

FIG. 9 is an illustration of an example computer system 1500 in whichembodiments of the present invention, or portions thereof, can beimplemented as computer-readable code.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

The invention is directed to correction of illumination irregularitiesin a lithography apparatus. It is particularly useful in a EUVlithography device. Embodiments of the invention are directed to linearmotors (actuators) forming part of an illumination irregularitycorrection (IIC) sub-system for correcting illumination irregularitiesand to a control system for operating the IIC sub-system. Embodiments ofthe IIC sub-system utilize an arrangement that does not require a largenumber of magnets as required by other IIC sub-systems. This portion ofthis patent document describes embodiments of the invention thatincorporate features of the invention. The described embodiments areexamples of the invention. The scope of the invention is not limited tothe described embodiment(s). The invention is defined by the claimsappended hereto.

The embodiments described, and references in the specification to “oneembodiment,” “an embodiment,” “an example embodiment,” etc., indicatethat the embodiment(s) described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

Before describing embodiments in more detail, it is instructive topresent an example environment in which embodiments of the presentinvention may be implemented.

I. An Example Lithographic Environment

A. Example Reflective and Transmissive Lithographic Systems

FIGS. 1A and 1B schematically depict lithographic apparatus 100 andlithographic apparatus 100′, respectively. Lithographic apparatus 100and lithographic apparatus 100′ each include: an illumination system(illuminator) IL configured to condition a radiation beam B (e.g., DUVor EUV radiation); a support structure (e.g., a mask table) MTconfigured to support a patterning device (e.g., a mask, a reticle, or adynamic patterning device) MA and connected to a first positioner PMconfigured to accurately position the patterning device MA; and asubstrate table (e.g., a substrate table) WT configured to hold asubstrate (e.g., a resist coated substrate) W and connected to a secondpositioner PW configured to accurately position the substrate W.Lithographic apparatuses 100 and 100′ also have a projection system PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion (e.g., comprising one or moredies) C of the substrate W. In lithographic apparatus 100 the patterningdevice MA and the projection system PS is reflective, and inlithographic apparatus 100′ the patterning device MA and the projectionsystem PS is transmissive.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic, or other types of optical components, or any combinationthereof, for directing, shaping, or controlling the radiation B. Theillumination system IL may also include an energy sensor ES thatprovides a measurement of the energy (per pulse), a measurement sensorMS for measuring the movement of the optical beam, and uniformitycompensators UC that allow the illumination slit uniformity to becontrolled.

The support structure MT holds the patterning device MA in a manner thatdepends on the orientation of the patterning device MA, the design ofthe lithographic apparatuses 100 and 100′, and other conditions, such asfor example whether or not the patterning device MA is held in a vacuumenvironment. The support structure MT may use mechanical, vacuum,electrostatic, or other clamping techniques to hold the patterningdevice MA. The support structure MT may be a frame or a table, forexample, which may be fixed or movable, as required. The supportstructure MT may ensure that the patterning device is at a desiredposition, for example with respect to the projection system PS.

The term “patterning device” MA should be broadly interpreted asreferring to any device that may be used to impart a radiation beam Bwith a pattern in its cross-section, such as to create a pattern in thetarget portion C of the substrate W. The pattern imparted to theradiation beam B may correspond to a particular functional layer in adevice being created in the target portion C, such as an integratedcircuit.

The patterning device MA may be transmissive (as in lithographicapparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus100 of FIG. 1A). Examples of patterning devices MA include reticles,masks, programmable mirror arrays, and programmable LCD panels. Masksare well known in lithography, and include mask types such as binary,alternating phase shift, and attenuated phase shift, as well as varioushybrid mask types. An example of a programmable mirror array employs amatrix arrangement of small mirrors, each of which may be individuallytilted so as to reflect an incoming radiation beam in differentdirections. The tilted mirrors impart a pattern in the radiation beam Bwhich is reflected by the mirror matrix.

The term “projection system” PS may encompass any type of projectionsystem, including refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or forother factors, such as the use of an immersion liquid or the use of avacuum. A vacuum environment may be used for EUV or electron beamradiation since other gases may absorb too much radiation or electrons.A vacuum environment may therefore be provided to the whole beam pathwith the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus 100 and/or lithographic apparatus 100′ may be ofa type having two (dual stage) or more substrate tables (and/or two ormore mask tables) WT. In such “multiple stages” machines the additionalsubstrate tables WT may be used in parallel or preparatory steps may becarried out on one or more tables while one or more other substratetables WT are being used for exposure.

Referring to FIGS. 1A and 1B, the illuminator IL receives a radiationbeam from a radiation source SO. The source SO and the lithographicapparatuses 100, 100′ may be separate entities, for example when thesource SO is an excimer laser. In such cases, the source SO is notconsidered to form part of the lithographic apparatuses 100 or 100′, andthe radiation beam B passes from the source SO to the illuminator ILwith the aid of a beam delivery system BD (FIG. 1B) comprising, forexample, suitable directing mirrors and/or a beam expander. In othercases, the source SO may be an integral part of the lithographicapparatuses 100, 100′—for example, when the source SO is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD, if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD (FIG. 1B) for adjustingthe angular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator may be adjusted. In addition, theilluminator IL may comprise various other components (FIG. 1B), such asan integrator IN and a condenser CO. The illuminator IL may be used tocondition the radiation beam B, to have a desired uniformity andintensity distribution in its cross section. This desired uniformity ismay be maintained through the use of the energy sensors ES thatdivides-out the variation of the source output and the uniformitycompensator UC that is comprised of a plurality of protrusions (e.g.,fingers) that can be inserted into and removed from the illuminationbeam to modify its uniformity and intensity.

Referring to FIG. 1A, the radiation beam B is incident on the patterningdevice (e.g., mask) MA, which is held on the support structure (e.g.,mask table) MT, and is patterned by the patterning device MA. Inlithographic apparatus 100, the radiation beam B is reflected from thepatterning device (e.g., mask) MA. After being reflected from thepatterning device (e.g., mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the radiation beam B onto atarget portion C of the substrate W. With the aid of the secondpositioner PW and position sensor IF2 (e.g., an interferometric device,linear encoder, or capacitive sensor), the substrate table WT may bemoved accurately, e.g. so as to position different target portions C inthe path of the radiation beam B. Similarly, the first positioner PM andanother position sensor IF1 may be used to accurately position thepatterning device (e.g., mask) MA with respect to the path of theradiation beam B. Patterning device (e.g., mask) MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2.

Referring to FIG. 1B, the radiation beam B is incident on the patterningdevice (e.g., mask MA), which is held on the support structure (e.g.,mask table MT), and is patterned by the patterning device. Havingtraversed the mask MA, the radiation beam B passes through theprojection system PS, which focuses the beam onto a target portion C ofthe substrate W. With the aid of the second positioner PW and positionsensor IF (e.g., an interferometric device, linear encoder, orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theradiation beam B. Similarly, the first positioner PM and anotherposition sensor (which is not explicitly depicted in FIG. 1B) can beused to accurately position the mask MA with respect to the path of theradiation beam B, e.g., after mechanical retrieval from a mask library,or during a scan. Likewise, in FIG. 2 there is a substrate stage slitsensor WS that on a per pulse basis in conjunction with the energysensor ES produces normalized intensity data from the illuminationsystem IL to the substrate W.

In general, movement of the mask table MT may be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of the first positioner PM.Similarly, movement of the substrate table WT may be realized using along-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to a scanner)the mask table MT may be connected to a short-stroke actuator only, ormay be fixed. Mask MA and substrate W may be aligned using maskalignment marks Ml, M2 and substrate alignment marks P1, P2. Althoughthe substrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (knownas scribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the mask MA, the mask alignment marks may belocated between the dies.

The lithographic apparatuses 100 and 100′ may be used in at least one ofthe following modes:

1. In step mode, the support structure (e.g., mask table) MT and thesubstrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam B is projected onto a targetportion C at one time (i.e., a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C may be exposed.

2. In scan mode, the support structure (e.g., mask table) MT and thesubstrate table WT are scanned synchronously while a pattern imparted tothe radiation beam B is projected onto a target portion C (i.e., asingle dynamic exposure). The velocity and direction of the substratetable WT relative to the support structure (e.g., mask table) MT may bedetermined by the (de-)magnification and image reversal characteristicsof the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is keptsubstantially stationary holding a programmable patterning device, andthe substrate table WT is moved or scanned while a pattern imparted tothe radiation beam B is projected onto a target portion C. A pulsedradiation source SO may be employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation may be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to herein.

Combinations and/or variations on the described modes of use or entirelydifferent modes of use may also be employed.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “substrate” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion,” respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

In a further embodiment, lithographic apparatus 100 includes an extremeultraviolet (EUV) source, which is configured to generate a beam of EUVradiation for EUV lithography. In general, the EUV source is configuredin a radiation system (see below), and a corresponding illuminationsystem is configured to condition the EUV radiation beam of the EUVsource.

B. Example EUV Lithographic Apparatus

FIG. 2 schematically depicts an exemplary EUV lithographic apparatusaccording to an embodiment of the present invention. In FIG. 2, EUVlithographic apparatus includes a radiation system 202, an illuminationoptics unit 204, and a projection system PS. The radiation system 202includes a radiation source SO, in which a beam of radiation may beformed by discharge plasma. In an embodiment, EUV radiation may beproduced by a gas or vapor, for example, from Xe gas, Li vapor, or Snvapor, in which very hot plasma is created to emit radiation in the EUVrange of the electromagnetic spectrum. The very hot plasma can becreated by generating at least partially ionized plasma by, for example,an electrical discharge. Partial pressures of, for example, 10 Pa of Xe,Li, Sn vapor or any other suitable gas or vapor may be required forefficient generation of the radiation. The radiation emitted byradiation source SO is passed from a source chamber 206 into a collectorchamber 208 via a gas barrier or contaminant trap 210 positioned in orbehind an opening in source chamber 206. In an embodiment, gas barrier210 may include a channel structure.

Collector chamber 208 includes a radiation collector 212 (which may alsobe called collector mirror or collector) that may be formed from agrazing incidence collector. Radiation collector 212 has an upstreamradiation collector side 214 and a downstream radiation collector side216, and radiation passed by collector 212 can be reflected off agrating spectral filter 218 to be focused at a virtual source point 220at an aperture in the collector chamber 208. Radiation collectors 212are known to skilled artisans.

From collector chamber 208, a beam of radiation 226 is reflected inillumination optics unit 204 via normal incidence reflectors 222 and 224onto a reticle or mask (not shown) positioned on reticle or mask tableMT. A patterned beam 228 is formed, which is imaged in projection systemPS via reflective elements 230 and 232 onto a substrate (not shown)supported on substrate stage or substrate table WT. In variousembodiments, illumination optics unit 204 and projection system PS mayinclude more (or fewer) elements than depicted in FIG. 2. For example,illumination optics unit 204 may also include an energy sensor ES thatprovides a measurement of the energy (per pulse), a measurement sensorMS for measuring the movement of the optical beam, and uniformitycompensators UC that allow the illumination slit uniformity to becontrolled. Additionally, grating spectral filter 218 may optionally bepresent, depending upon the type of lithographic apparatus. Further, inan embodiment, illumination optics unit 204 and projection system PS mayinclude more mirrors than those depicted in FIG. 2. For example,projection system PS may incorporate one to four reflective elements inaddition to reflective elements 230 and 232. In FIG. 2, reference number240 indicates a space between two reflectors, e.g., a space betweenreflectors 234 and 236.

In an embodiment, collector mirror 212 may also include a normalincidence collector in place of or in addition to a grazing incidencemirror. Further, collector mirror 212, although described in referenceto a nested collector with reflectors 234, 236, and 238, is hereinfurther used as example of a collector.

Further, instead of a grating 218, as schematically depicted in FIG. 2,a transmissive optical filter may also be applied. Optical filterstransmissive for EUV, as well as optical filters less transmissive foror even substantially absorbing UV radiation, are known to skilledartisans. Hence, the use of “grating spectral purity filter” is hereinfurther indicated interchangeably as a “spectral purity filter,” whichincludes gratings or transmissive filters. Although not depicted in FIG.2, EUV transmissive optical filters may be included as additionaloptical elements, for example, configured upstream of collector mirror212 or optical EUV transmissive filters in illumination unit 204 and/orprojection system PS.

The terms “upstream” and “downstream,” with respect to optical elements,indicate positions of one or more optical elements “optically upstream”and “optically downstream,” respectively, of one or more additionaloptical elements. Following the light path that a beam of radiationtraverses through lithographic apparatus, a first optical elementscloser to source SO than a second optical element is configured upstreamof the second optical element; the second optical element is configureddownstream of the first optical element. For example, collector mirror212 is configured upstream of spectral filter 218, whereas opticalelement 222 is configured downstream of spectral filter 218.

All optical elements depicted in FIG. 2 (and additional optical elementsnot shown in the schematic drawing of this embodiment) may be vulnerableto deposition of contaminants produced by source SO, for example, Sn.Such may be the case for the radiation collector 212 and, if present,the spectral purity filter 218. Hence, a cleaning device may be employedto clean one or more of these optical elements, as well as a cleaningmethod may be applied to those optical elements, but also to normalincidence reflectors 222 and 224 and reflective elements 230 and 232 orother optical elements, for example additional mirrors, gratings, etc.

Radiation collector 212 can be a grazing incidence collector, and insuch an embodiment, collector 212 is aligned along an optical axis O.The source SO, or an image thereof, may also be located along opticalaxis O. The radiation collector 212 may comprise reflectors 234, 236,and 238 (also known as a “shell” or a Wolter-type reflector includingseveral Wolter-type reflectors). Reflectors 234, 236, and 238 may benested and rotationally symmetric about optical axis O. In FIG. 2, aninner reflector is indicated by reference number 234, an intermediatereflector is indicated by reference number 236, and an outer reflectoris indicated by reference number 238. The radiation collector 212encloses a certain volume, e.g., a volume within the outer reflector(s)238. Usually, the volume within outer reflector(s) 238 iscircumferentially closed, although small openings may be present.

Reflectors 234, 236, and 238 respectively may include surfaces of whichat least a portion represents a reflective layer or a number ofreflective layers. Hence, reflectors 234, 236, and 238 (or additionalreflectors in the embodiments of radiation collectors having more thanthree reflectors or shells) are at least partly designed for reflectingand collecting EUV radiation from source SO and at least part ofreflectors 234, 236, and 238 may not be designed to reflect and collectEUV radiation. For example, at least part of the back side of thereflectors may not be designed to reflect and collect EUV radiation. Onthe surface of these reflective layers, there may be in addition a caplayer for protection or as an optical filter provided on at least partof the surface of the reflective layers.

The radiation collector 212 may be placed in the vicinity of the sourceSO or an image of the source SO. Each reflector 234, 236, and 238 maycomprise at least two adjacent reflecting surfaces, the reflectingsurfaces further from the source SO being placed at smaller angles tothe optical axis O than the reflecting surface that is closer to thesource SO. In this way, a grazing incidence collector 212 is configuredto generate a beam of EUV radiation propagating along the optical axisO. At least two reflectors may be placed substantially coaxially andextend substantially rotationally symmetric about the optical axis O. Itshould be appreciated that radiation collector 212 may have furtherfeatures on the external surface of outer reflector 238 or furtherfeatures around outer reflector 238, for example a protective holder, aheater, etc.

In the embodiments described herein, the terms “lens” and “lenselement,” where the context allows, may refer to any one or combinationof various types of optical components, comprising refractive,reflective, magnetic, electromagnetic and electrostatic opticalcomponents.

Further, the terms “radiation” and “beam” used herein encompass alltypes of electromagnetic radiation, comprising ultraviolet (UV)radiation (e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm),extreme ultra-violet (EUV or soft X-ray) radiation (e.g., having awavelength in the range of 5-20 nm, e.g., 13.5 nm), or hard X-rayworking at less than 5 nm, as well as particle beams, such as ion beamsor electron beams. Generally, radiation having wavelengths between about780-3000 nm (or larger) is considered IR radiation. UV refers toradiation with wavelengths of approximately 100-400 nm. Withinlithography, it is usually also applied to the wavelengths, which can beproduced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm;and/or I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by air),refers to radiation having a wavelength of approximately 100-200 nm.Deep UV (DUV) generally refers to radiation having wavelengths rangingfrom 126 nm to 428 nm, and in an embodiment, an excimer laser cangenerate DUV radiation used within lithographic apparatus. It should beappreciated that radiation having a wavelength in the range of, forexample, 5-20 nm relates to radiation with a certain wavelength band, ofwhich at least part is in the range of 5-20 nm.

II. System and Methods for Illumination Irregularity Compensation (IIC)

FIG. 3 is an exploded view of a mechanical portion of an IIC sub-system300, according to an embodiment. IIC sub-system 300 has 28 movingfingers 302, each having a fingertip 304, which selectively block asmall portion of the illumination beam prior to exposure to correct forillumination irregularities and to provide a uniform beam in the crossscan direction. Each finger 302 is supported by a single finger assembly306 which includes a magnet 308. The single finger assemblies 306together form a finger assembly 310. IIC sub-system 300 includes a frame312 for holding and supporting finger assembly 310 and the rest of theparts of IIC sub-system 300 using mounts 314. A motor coil assembly 316moves single finger assemblies 306 into proper position to compensatefor illumination irregularities as needed and out of the way when notneeded. IIC sub-system 300 also includes finger flexures 318 and afinger stop 320 to stop the motion of finger assemblies 306 at extremepositions. An encoder board assembly 330 provides anelectrical/mechanical interface for encoding the mechanical position offinger assemblies 306 and provide instructions to motor coil assembly316.

The configuration of IIC sub-system 300 requires 112 magnets, four foreach finger assembly 36. These magnets are made of neodymium iron boronand need to be protected from the H2 environment of an extremeultra-violet (EUV) scanner to prevent failure of the magnets. Protectingthe magnets 308 is difficult to achieve for EUV lithography scannersbecause the magnets must be maintained within a vacuum. While IICsub-system 300 operates effectively, the use of 112 magnets per IICsub-system 300 requires expensive maintenance when any magnet failsbecause of its complex construction. Each time maintenance is required,a recalibration is required. The motor design also requires a flat coilplate with 28 coils arranged in a common plane. This presentsmanufacture challenges to achieve the overall flatness and outgassingrequired. An additional complexity is that IIC sub-system 300 requiresthe 28 fingers 302 to wrap around the coil plate of motor coil assembly316. This presents dynamics challenges.

FIG. 4 is a cut-away perspective view of the structure of a portion 400of IIC sub-system 300 shown in FIG. 3. In this cut-away view it ispossible to see inner edges 402 of four magnets 308. The direction oftravel of portion 400 is indicated by arrow 404. Coils of motor coilassembly 316 are indicated by 406. A direction of travel is indicated byarrow 408.

FIG. 5 is a block diagram of a servo control system 500 for operatingIIC sub-system 300 shown in FIGS. 3 and 4. Physical connections orsoftware relations are indicated by a solid line arrow. Virtualrelations are indicated by a dotted line arrow. A set point generator502 sets a desired finger position and sends a signal carrying thatinformation to a feed forward position velocity acceleration block 504.Set point generator 502 also sends a similar signal to a comparator 506,which compares it with a signal representing an actual finger positionfrom encoder electronics 508. Encoder electronics 508 is mounted on anencoder head 510 and reads relative position between encoder head 510and an encoder scale 512. Encoder read head 510 receives its controlsignal from an encoder assembly 514. A comparator 516 receives inputsfrom encoder read head 510 and encoder scale 512 and provides a signalto encoder electronics 508.

An output signal 506 from comparator 516 is coupled to a controller andfilter 518. A further comparator 520 compares an output of control andfilter 518 with an output of feed forward position velocity accelerationblock 504 and provides a signal to a filter 522. An output of filter 522is coupled to a TAPA 524 which, in turn, provides a control signal tocoil plate 526. Coil plate 526 also receives an input from a Unicom NXEframe 528 and provides control to a magnet assembly 530. Unicom NXEframe 528 also provides a signal to encoder assembly 514 and to a fingerassembly 532. Finger assembly 532 is also controlled by magnet assembly530 and, in turn, provides an output 534 indicating fingertip position.An ILL frame 540 provides input to Unicom NXE frame 528. Encoder scale512 receives input from finger assembly 534.

The market demands that sub-systems for manipulating the positions offingers reliably operate in the environment of a lithography device sothat the lithographic apparatus can perform lithography processes asefficiently as possible to maximize manufacturing capacity and keepcosts per device and maintenance low. The present invention providesvarious apparatus, methods and arrangements that can be used to satisfythis market demand.

An embodiment of the invention is a lithographic apparatus. Anillumination system is configured to condition a beam of radiation. Asupport structure is configured to hold a patterning device which isconfigured and arranged to pattern the conditioned beam of radiation. Asubstrate table is configured and arranged to hold a substrate on whicha lithographic process is to be carried out. A projection systemprojects a patterned radiation beam onto a target portion of thesubstrate. An illumination irregularity correction system is located ina plane and is configured to receive a substantially constant pupil whenilluminated with the beam of radiation. Fingers of the uniformitycorrection system are configured and arranged to be movable into and outof intersection with a radiation beam so as to correct an intensity ofrespective portions of the radiation beam. Actuating devices are coupledto corresponding ones of the fingers and are configured to move thecorresponding fingers. An actuation device includes a fixed statorhaving first, second and third poles disposed on a plane in a spatialsequence. The first and third poles have a coil wound thereon. Theactuation device also includes a rotor having fourth and fifth polesdisposed in the plane. The rotor is constructed and arranged to belinearly movable in two dimensions when the first, second and thirdpoles of the fixed stator become energized in response to the coilswound on the first and third poles being energized in a temporalsequence. The fourth and fifth poles are disposed opposite the first,second and third poles and the fixed stator is constructed and arrangedto be fixed relative to the rotor. The rotor can be constructed andarranged to position at least one finger of the fingers in response toadjusting of a current in each of the coils in micro steps. Current ineach coil can be adjusted with sine cosine microstepping. The fixedstator can be made of iron. The rotor can also be made of iron.

The lithography system can further include a servo control systemconstructed and arranged to control the actuating devices. The servocontrol system includes a module constructed and arranged to set adesired position of a finger. Another module is constructed and arrangedto sense a present position of the finger. Another module is constructedand arranged to generate currents appropriate to control the position ofthe finger such that it is positioned at the desired position.

Another embodiment of the invention provides a linear switchedreluctance motor. A stator of the motor has a fixed coil arrangement,the stator including at least three poles disposed on a plane in aspatial sequence. A rotor of the motor includes at least two polesdisposed in the plane, the rotor being constructed and arranged to belinearly movable in two dimensions by the fixed coil arrangement. Thestator is constructed and arranged to remain stationary relative to therotor. The two rotor poles are disposed opposite the three stator poles.The fixed coil arrangement can include windings on each of at least twopoles of the stator.

An embodiment of the invention provides a linear switched reluctancemotor. A fixed stator of the motor including first, second and thirdpoles disposed on a plane in a spatial sequence, wherein the first andthird poles having a coil wound thereon. A rotor of the motor includesfourth and fifth poles disposed in the plane, the rotor beingconstructed and arranged to be linearly movable in two dimensions whenthe first, second and third poles of the fixed stator become energizedin response to the coils wound on the first and third poles beingenergized in a temporal sequence. The fourth and fifth poles of therotor are disposed opposite the first, second and third poles of thefixed stator which is arranged to be fixed relative to the rotor. Therotor may be coupled to a finger such that the position of the fingercan be controlled in response to adjusting of a current in each of thecoils in micro steps. Current in the coils may be adjusted with sinecosine microstepping.

An embodiment of the invention is directed to an illuminationirregularity correction system (IICS) located at a plane configured toreceive a substantially constant pupil when illuminated with a beam ofradiation. The IICS includes a plurality of fingers configured to bemovable into and out of intersection with a radiation beam so as tocorrect an intensity of respective portions of the radiation beam. Aplurality of actuating devices coupled to corresponding ones of thefingers are configured and arranged to move the corresponding fingers.An actuating device includes a fixed stator including first, second andthird poles disposed on a plane in a spatial sequence. The first andthird poles having a coil wound thereon. The actuating device alsoincludes a rotor having fourth and fifth poles disposed in the plane.The rotor is constructed and arranged to be linearly movable in twodimensions when the first, second and third poles of the fixed statorbecome energized in response to the coils wound on the first and thirdpoles being energized in a temporal sequence. The fourth and fifth polesof the rotor are disposed opposite the first, second and third poles andthe fixed stator is constructed and arranged to be fixed relative to therotor. The rotor may be constructed and arranged to position at leastone finger in response to adjusting of a current in each of the coils inmicro steps. Current in the each of the coils may be adjusted with sinecosine microstepping.

An embodiment of the invention provides a method for correctingillumination irregularity in a radiation beam of a lithography system.An IICS is located at a plane and is configured to receive asubstantially constant pupil when illuminated with a beam of radiation.A plurality of fingers are provided and configured to be movable intoand out of intersection with the radiation beam so as to correct anintensity of respective portions of the radiation beam. A plurality ofactuating devices are coupled to corresponding ones of the fingers, theplurality of actuating devices being configured to move thecorresponding fingers. An actuation device is configured to have a fixedstator including first, second and third poles disposed on a plane in aspatial sequence, wherein the first and third poles having a coil woundthereon. A rotor includes fourth and fifth poles disposed in the plane,the rotor is constructed and arranged to be linearly movable in twodimensions when the first, second and third poles of the fixed statorbecome energized in response to the coils wound on the first and thirdpoles being energized in a temporal sequence. The fourth and fifth polesare disposed opposite the first, second and third poles. The fixedstator is constructed and arranged to be fixed relative to the rotor.Current may be adjusted in each of the coils in micro steps to cause therotor to position at least one finger of the fingers in response to theadjusting of the current. Adjusting a current in each of the coils inmicro steps may include adjusting the current in the each of the coilswith sine cosine microstepping.

An embodiment of the invention is directed to a linear switchedreluctance motor. A stator has a fixed coil arrangement, the statorincluding at least two poles disposed on a plane in a spatial sequence.A rotor includes at least one pole disposed in the plane, the rotorbeing constructed and arranged to be linearly movable in two dimensionsby the fixed coil arrangement. The stator is constructed and arranged toremain stationary relative to the rotor. The rotor pole is disposedopposite the stator's two poles. The fixed coil arrangement may furtherinclude a coil wound on each of the two poles.

An embodiment of the invention provides a lithographic apparatusincluding an illumination system configured to condition a beam ofradiation. A support structure is configured and arranged to hold apatterning device which is configured to pattern the conditioned beam ofradiation. A substrate table is configured to hold a substrate on whichlithography is to be performed. A projection system is configured andarranged to project the patterned radiation beam onto a target portionof the substrate. An optical system is located within the illuminationsystem and includes an actuation device. The actuation device includes afixed stator having first, second and third poles disposed on a plane ina spatial sequence, wherein the first and third poles having a coilwound thereon. A rotor includes fourth and fifth poles disposed in theplane, the rotor being constructed and arranged to be linearly movablein two dimensions when the first, second and third poles of the fixedstator become energized in response to the coils wound on the first andthird poles being energized in a temporal sequence, wherein the fourthand fifth poles of the rotor are disposed opposite the first, second andthird poles of the stator and the fixed stator is constructed andarranged to be fixed relative to the rotor.

An embodiment of the invention provides a lithographic apparatusincluding an illumination system configured to condition a beam ofradiation. A support structure is configured to hold a patterningdevice, the patterning device being configured and arranged to patternthe conditioned beam of radiation. A substrate table is arranged to holda substrate on which lithography is to be performed. A projection systemis configured and arranged to project the patterned radiation beam ontoa target portion of the substrate. An optical system is located withinthe projection system. The optical system includes an actuation device.The actuation devices includes a fixed stator having first, second andthird poles disposed on a plane in a spatial sequence, wherein the firstand third poles having a coil wound thereon. A rotor includes fourth andfifth poles disposed in the plane, the rotor being constructed andarranged to be linearly movable in two dimensions when the first, secondand third poles of the fixed stator become energized in response to thecoils wound on the first and third poles being energized in a temporalsequence. The fourth and fifth poles of the rotor are disposed oppositethe first, second and third poles of the stator. The stator isconstructed and arranged to be fixed relative to the rotor. Some of theembodiments will be described with respect to drawings below.

FIG. 6 is a schematic diagram of an embodiment of a linear motorarrangement that can be substituted for a portion of the compensatorsub-system shown in FIGS. 3 and 4. An iron “stator” 602 has three poles604, 606, 608 and two coils 610, 612. A movable iron “rotor” 620 ispositioned based on forces 622, 624 controlled by energizing coils 610and 612. By adjusting the current in each of coils 610 and 612 theposition of rotor 620 can be accurately controlled. This can be donewith “sine cosine micro stepping” a rotary stepper motor. In turn, theposition of a finger body 630, attached to rotor 620 can be controlledto move along a direction indicated by arrow 632. This configuration isdetermined primarily by existing packaging of an assembly intended for acurrent design EUV lithography apparatus having a short +/−3 mm travelachieved within one “step.” Other configurations are possible. Thisconfiguration shown and described above eliminates the need for a fingerbody to wrap around a coil plate (as in the FIG. 3 and FIG. 4arrangements and allows a thick coil plate with embedded water cooling.This configuration can be used in other lithography modules as well toeliminate magnets from within an H2 environment.

By placing a current in coil 610 in a given direction, say clockwise anda current in coil 612 in the opposite direction, say counterclockwise, amagnetic flux will be driven through the poles of stator 602 and throughthe poles of rotor 620. This will apply a force on rotor 620 to alignits poles with the poles of stator 602, effectively driving finger body630. Applying current in opposite directions drive the finger body inthe opposite direction.

FIG. 7 is a schematic diagram of another embodiment of a linear motorarrangement that can be substituted for a portion of the compensatorsub-system shown in FIGS. 3 and 4. This embodiment is similar to theembodiment shown in FIG. 6, but has three coils 710, 712 and 714 ratherthan only two. The use of an additional coil provides a finer controlover the position of rotor 620 and therefore finger body 630.

This principle of operation of the embodiments shown in FIGS. 6 and 7apply to many configurations including a two pole rotor paired with atwo pole, single coil stator which can only apply a force in onedirection (e.g. to position a finger body against a spring).

FIG. 8 is a block diagram of a control system 800 for operating an IICsubsystem including the embodiments shown in FIGS. 6 and 7. As in FIG.5, physical connections or software relations are indicated by a solidline arrow. Virtual relations are indicated by a dotted line arrow. Withrespect to control system 500 shown in FIG. 5, TAPA 524 is replaced byan amplifier 824, coil plate 526 is replaced by coil and statorassembly, and magnet assembly 530 is replaced by iron “rotor” 830. Inother respects, the servo system operates in a similar fashion to thatof servo system 500 shown in FIG. 5. The blocks of control system 800cooperate to form a module constructed and arranged to set a desiredposition of a finger; a module constructed and arranged to sense apresent position of the finger; and a module constructed and arranged togenerate currents appropriate to control the position of the finger suchthat it is positioned at the desired position.

FIG. 9 is an illustration of an example computer system 900 in whichembodiments of the present invention, or portions thereof, can beimplemented as computer-readable code. The control arrangements andmethods illustrated in FIGS. 5 and 8 can be implemented ascomputer-readable code. They can also be implemented in computer system900 that includes a display interface 902 coupled to a display 930.Various embodiments of the invention are described in terms of thisexample computer system 900. After reading this description, it willbecome apparent to a person skilled in the relevant art how to implementembodiments of the invention using other computer systems and/orcomputer architectures.

Computer system 900 includes one or more processors, such as processor904. Processor 904 may be a special purpose or a general purposeprocessor. Processor 904 is connected to a communication infrastructure906 (e.g., a bus or network).

Computer system 900 also includes a main memory 905, preferably randomaccess memory (RAM), and may also include a secondary memory 910.Secondary memory 910 can include, for example, a hard disk drive 912, aremovable storage drive 914, and/or a memory stick. Removable storagedrive 914 can comprise a floppy disk drive, a magnetic tape drive, anoptical disk drive, a flash memory, or the like. The removable storagedrive 914 reads from and/or writes to a removable storage unit 918 in awell-known manner. Removable storage unit 918 can include a floppy disk,magnetic tape, optical disk, etc. which is read by and written to byremovable storage drive 914. As will be appreciated by persons skilledin the relevant art, removable storage unit 918 includes acomputer-usable storage medium having stored therein computer softwareand/or data.

In alternative implementations, secondary memory 910 can include othersimilar devices for allowing computer programs or other instructions tobe loaded into computer system 900. Such devices can include, forexample, a removable storage unit 918 and an interface 920. Examples ofsuch devices can include a program cartridge and cartridge interface(such as those found in video game devices), a removable memory chip(e.g., EPROM or PROM) and associated socket, and other removable storageunits 918 and interfaces 920 which allow software and data to betransferred from the removable storage unit 918 to computer system 900.

Computer system 900 can also include a communications interface 924.Communications interface 924 allows software and data to be transferredbetween computer system 900 and external devices. Communicationsinterface 924 can include a modem, a network interface (such as anEthernet card), a communications port, a PCMCIA slot and card, or thelike. Software and data transferred via communications interface 924 arein the form of signals, which may be electronic, electromagnetic,optical, or other signals capable of being received by communicationsinterface 924. These signals are provided to communications interface924 via a communications path 926 and 928. Communications path 926 and928 carries signals and may be implemented using wire or cable, fiberoptics, a phone line, a cellular phone link, a RF link or othercommunications channels.

In this document, the terms “computer program medium” and“computer-usable medium” are used to generally refer to media such asremovable storage unit 918, removable storage unit 918, and a hard diskinstalled in hard disk drive 912. Computer program medium andcomputer-usable medium can also refer to memories, such as main memory905 and secondary memory 910, which can be memory semiconductors (e.g.,DRAMs, etc.). These computer program products provide software tocomputer system 900.

Computer programs (also called computer control logic) are stored inmain memory 905 and/or secondary memory 910. Computer programs may alsobe received via communications interface 924. Such computer programs,when executed, enable computer system 900 to implement embodiments ofthe present invention as discussed herein. In particular, the computerprograms, when executed, enable processor 904 to implement processes ofthe present invention, discussed above. Accordingly, such computerprograms represent controllers of the computer system 900. Whereembodiments of the invention are implemented using software, thesoftware can be stored in a computer program product and loaded intocomputer system 900 using removable storage drive 914, interface 920,hard drive 912 or communications interface 924.

Embodiments of the invention are also directed to computer programproducts including software stored on any computer-usable medium. Suchsoftware, when executed in one or more data processing device, causes adata processing device(s) to operate as described herein. Embodiments ofthe invention employ any computer-usable or -readable medium, known nowor in the future. Examples of computer-usable mediums include, but arenot limited to, primary storage devices (e.g., any type of random accessmemory), secondary storage devices (e.g., hard drives, floppy disks, CDROMS, ZIP disks, tapes, magnetic storage devices, optical storagedevices, MEMS, Nano technological storage devices, etc.), andcommunication mediums (e.g., wired and wireless communications networks,local area networks, wide area networks, intranets, etc.).

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, the Examiner is also reminded that anydisclaimer made in the instant application should not be read into oragainst the parent application.

What is claimed is:
 1. A linear switched reluctance motor comprising: astator having a fixed coil arrangement, the stator including at leastthree poles disposed on a plane in a spatial sequence; and a rotorincluding at least two poles disposed in the plane, the rotorconstructed and arranged to be linearly movable in two dimensions by thefixed coil arrangement while the stator is constructed and arranged toremain stationary relative to the rotor, wherein the at least two polesare disposed opposite the at least three poles.
 2. The linear switchedreluctance motor according to claim 1, wherein the fixed coilarrangement further comprising a coil wound on each of at least twopoles of the at least three poles.
 3. A linear switched reluctance motorcomprising: a fixed stator including first, second and third polesdisposed on a plane in a spatial sequence, wherein the first and thirdpoles having a coil wound thereon; and a rotor including fourth andfifth poles disposed in the plane, the rotor constructed and arranged tobe linearly movable in two dimensions when the first, second and thirdpoles of the fixed stator become energized in response to the coilswound on the first and third poles being energized in a temporalsequence, wherein the fourth and fifth poles are disposed opposite thefirst, second and third poles and the fixed stator is constructed andarranged to be fixed relative to the rotor.
 4. The linear switchedreluctance motor according to claim 3, wherein the rotor is coupled to afinger, the rotor is constructed and arranged to position the finger inresponse to adjusting of a current in each of the coils in micro steps.5. The linear switched reluctance motor according to claim 4, whereinthe current in the each of the coils is adjusted with sine cosinemicrostepping.
 6. A linear switched reluctance motor comprising: astator having a fixed coil arrangement, the stator including at leasttwo poles disposed on a plane in a spatial sequence; and a rotorincluding at least one pole disposed in the plane, the rotor constructedand arranged to be linearly movable in two dimensions by the fixed coilarrangement while the stator is constructed and arranged to remainstationary relative to the rotor, wherein the at least one pole isdisposed opposite the at least two poles.
 7. The linear switchedreluctance motor according to claim 6, wherein the fixed coilarrangement further comprising a coil wound on each of the at least twopoles.